Saturday, August 27, 2011

Darwin's Finches

Male Medium Ground Finch - Rabida Island
All right, we've been home from the Galapagos for two weeks, and I've posted something here almost every day. But I have not written about the famous finches that inspired Darwin on the theory of evolution. But remember, I have trouble identifying Little Brown Jobs in any event, and they didn't all evolve from one species of birds!

Medium Ground Finch Female
In 1831, Charles Darwin was a 22-year-old who vomited in medical school classes, and began studying at Cambridge to enter the Church of England, when botanist John Henslow introduced him to the natural world. Henslow then introduced him to Captain Robert FitzRoy of HMS Beagle, and he joined on for the five year voyage as a companion and budding naturalist. Henslow also advised young Charles to read Charles Lyell's Principles of Geology, but told him 'on no account accept the views therein advocated.' Lyell described a world where land forms were constantly moving and changing. As Darwin observed volcanoes in various locations, he saw that the land was new in the Galapagos, and life had come later.
Medium Ground Finch Females - Rabida Island
Like all naturalists of the era, Darwin "collected" his samples, birds, lizard, plants, tortoises, amazed at their tameness. He noted, "I have specimens from four of the larger Islands...The specimens from Chatham and Albemarle Isd. appear to be the same; but the other two are different. In each Isd. each kind is exclusively found." It didn't take long for him to notice the changes from island to island for each species.
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In 1836 he and the Beagle returned home, and he gave his collected birds to ornithologist John Gould, who quickly concluded, "...that he was induced to regard them as constituting an entirely new group, containing 13 species, and appearing to be strictly confined to the Galapagos Islands...their principle peculiarity consisted in the bill presenting several distinct modifications of form." Unfortunately, Darwin had failed to mark the island of origin, having identified the different looking birds as other species familiar from home. Well, others in the crew had been more meticulous, so "natural selection" came into being with the help of finches, mockingbirds and tortoises. And the rest, as they say, is history, or evolution!
Male Ground Finch
I learned from Darwin, and carefully saved my photos according to the islands where they were taken. But to me, the finches are just more LBJs. They were not afraid of us, and filled the paths as we walked, blending with the color of the rocks. The males are black and the females brown with strips. So far, so good. I can tell them apart by gender. A flock of little ground finches flew almost between our legs to get the best seeds from the grass.

Female Medium Cactus Finch Santa Cruz
The part I couldn't get a feel for was the sizing.  Most finches are called Large, Medium and Small depending on the size of their beaks!  We saw this one actually eating cactus on Santa Cruz, and felt comfortable with it being a Cactus Finch. So there are Large, Medium and Small Ground Finches and Tree Finches. Rounding up the total is the Sharp-beaked Ground-Finch (only found on three islands we did not visit), the Vegetarian Finch (again, limited to just two islands), Mangrove Finch (only on Isabela), Woodpecker Finch and Warbler Finch. Just from their names, you get a feel for what they eat.
Male Large Cactus Finch Espanola
But Kevin identified this bird as a Large Cactus Finch.  Look at the beaks on each bird, and notice the difference.

Adaptive Radiation is the name for this process. Because the finches were isolated on each island, they had to change to survive in the conditions of that island. For finches, the change involved the size of the beak changing for the food available on the island.
Female Warbler Finch
 Did I ever mention how glad I am not to be an ornithologist in charge of determining the species of a newly found bird?

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